1. Technical Field
This disclosure relates to the administration of pharmaceutical substances, typically intrinsically harmful or toxic pharmaceutical substances such as radioactive pharmaceutical substances, generally known as radiopharmaceuticals, to human and animal subjects and, more specifically, to a method of and a system for measuring the activity of a radiopharmaceutical during an injection procedure.
2. Description of Related Art
Administration of radioactive pharmaceutical substances or drugs, generally termed radiopharmaceuticals, is often used in the medical field to provide information or imagery of internal body structures and/or functions including, but not limited to, bone, vasculature, organs and organ systems, and other tissue. Additionally, such radiopharmaceuticals may be used as therapeutic agents to kill or inhibit the growth of targeted cells or tissue, such as cancer cells.
Two types of imaging procedures utilizing radiopharmaceuticals are positron emission tomography (PET) or single-photon emission computerized tomography (SPECT) procedures. PET and SPECT are noninvasive, three-dimensional, imaging procedures that provide information regarding physiological and biochemical processes in patients. PET and SPECT images of, for example, the brain or another organ, are produced by injecting the patient with a dose of a radiopharmaceutical and then creating an image based on the radiation emitted by the radiopharmaceutical. The radiopharmaceutical generally includes a radioactive substance, such as a radioisotope, that can be absorbed by certain cells in the brain or other organs, concentrating it there.
Radioisotopes, especially those with short half-lives, can be relatively safely administered to patients in the form of a labeled substrate, ligand, drug, antibody, neurotransmitter, or other compound or molecule that is normally processed or used by the body (for example, glucose). The radioisotope acts as a tracer of specific physiological or biological processes. For example, fluorodeoxyglucose (FDG) is a normal molecule of glucose, the basic energy fuel of cells, to which is attached a radioisotope or radioactive fluorine (i.e., 18F). The 18F radioisotope is produced in a cyclotron equipped with a unit to synthesize the FDG molecule.
Cells (for example, in the brain) that are more active in a given period of time after an injection of FDG will absorb more FDG because they have a higher metabolism and require more energy. The 18F radioisotope in the FDG molecule experiences a radioactive decay, emitting a positron. When a positron collides with an electron, annihilation occurs, liberating a burst of energy in the form of two beams of gamma rays in opposite directions. The PET scanner detects the emitted gamma rays to compile a three dimensional image.
To allow for cell uptake of the radiopharmaceutical, the patient typically rests for a period of time (45-90 minutes for FDG) after the radiopharmaceutical is injected. After sufficient time for cell uptake has elapsed, the patient is typically placed on a movable bed that slides into the PET (or SPECT), or other suitable scanner. The PET scanner includes several rings of radiation detectors. Each detector emits a brief pulse of light every time it is struck with a gamma ray coming from the radioisotope within the patient's body. The pulse of light is amplified by, for example, a photomultiplier, and the information is sent to the computer for forming images of the patient.
To minimize the radiation dose to patients, radiopharmaceuticals containing radioisotopes, such as Flourine-18, Technetium-99, Carbon-11, Copper-64, Gallium-67, Iodine-123, Nitrogen-13, Oxygen-15, Rubidium-82, Thallium-201, Chromium-51, Iodine-131, Iodine-151, Iridium-192, Phosphorus-32, Samarium-153, and Yttrium-90, having relatively short half-lives are typically used for PET and SPECT imaging procedures and other radio-therapies. 18F, for example, has a half-life of 109.7 minutes.
Because of its short half-life, the radioactivity level of the radioisotope will quickly decrease after it is manufactured in a cyclotron or a reactor. Consequently, the elapsed time (and corresponding decrease in radioactivity level of the radioisotope) after synthesis of the radiopharmaceutical must be factored into calculating the volume of radiopharmaceutical required to be injected into the patient to deliver the desired radioactivity dose. If the time delay after synthesis is long in relation to the radioisotope's half-life or if the calculated volume of radiopharmaceutical to be injected into the patient is insufficient to deliver the desired radioactivity dose, the delivered radioactivity dose may be too low to provide diagnostic-quality images, resulting in wasted time and effort and exposing the patient and medical personnel to unnecessary radiation.
In addition, radiopharmaceutical agents used in imaging procedures and therapeutic procedures are hazardous to attending medical personnel. These agents are toxic and can have physical and/or chemical effects for attending medical personnel such as clinicians, imaging technicians, nurses, and pharmacists. Excessive radiation exposure is harmful to attending medical personnel due to their occupational repeated exposure to the radiopharmaceuticals. However, due to the short half-life of typical radiopharmaceutical agents and small applied dosages, the radiation exposure risk-to-benefit ratio for individual patients is acceptable. The constant and repeated exposure of medical personnel to radiopharmaceuticals over an extended period of time is a significant problem in the nuclear medicine field.
With the foregoing background in place, exemplary current practice of generating, preparing, and administration of radiopharmaceuticals will now be described. Typical radiopharmaceutical treatment practice in the United States includes having the radiopharmaceutical agent initially generated off-site from a treatment location, typically a hospital, by an outside nuclear medicine facility and then delivered to the treatment location for further preparation, for example, individual dosing and administration. The treatment location, for example, a hospital, orders specific radioactive substances to be ready at specific times for specific patients. These substances are prepared by the outside nuclear medicine facility and with sufficient radioactivity that they will have the desired radioactivity level at the targeted time. For example, the outside nuclear medicine provider may have a facility equipped with a cyclotron or radioisotope generator in, for example, a lead-shielded enclosure wherein the radiopharmaceutical agent, namely, a radioactive isotope is generated or created. Further refining or dose preparation steps, namely, placing the radioisotope in injectable form, may occur at the off-treatment site. Thus, the outside provider may provide a radiopharmaceutical substance to the treatment site having a desired radioactivity level at the targeted time. Further “individual” dose preparation of the radiopharmaceutical agent may occur at the treatment site. Alternatively, the outside provider may provide a “finished” radiopharmaceutical agent ready for injection to a specified patient at a specified time so that treatment site personnel are only required to confirm that the correct radioactive dosage is present in the radiopharmaceutical agent, for example, in a stand-alone radiation dosimetry device as described previously. During the forgoing process, there is frequent close-proximity contact with radioactive materials by personnel and, as described previously, handling and transport shielding devices are needed for the protection of these personnel.
Transport pigs are commonly employed to transport the radiopharmaceutical agents, which are individual doses prepared for individual patients, to the treatment facility. At the treatment facility, data about each unit dose is entered into a facility computer either manually or through reading a bar code, floppy disk, or other similar data format, which may accompany or be on the transport pig or the radiopharmaceutical agent container. When it is time to deliver a specified unit dose to a specified patient, treatment facility personnel must remove, for example, a syringe containing the radiopharmaceutical agent from the transport pig and confirm that the dose in the syringe is within the range prescribed for that patient. Alternatively, the attending personnel must transfer the radiopharmaceutical agent to a shielded syringe as identified previously and confirm dosage. If the dose is too high, some is discarded into a shielded waste container. If the dose is too low, either a different syringe is used and/or additional agent is loaded into the syringe if available. While it is possible for the attending treatment site personnel to be involved with dosage preparation, typical United States practice is to have the radiopharmaceutical agent delivered to the treatment site which will have the desired radioactivity level at the targeted time. Manual manipulation of the radiopharmaceutical agent at the treatment site is limited at the treatment site due to this procedure. Nonetheless, various manual checks are required to confirm that a correct radiopharmaceutical dose is ready for injection into a specific patient. These manual checks include visual inspections and radioactivity measurements as noted above.
As an example of the foregoing, in PET imaging, an injectable radiopharmaceutical agent such as, for instance, FDG (fluorodeoxyglucose) is fabricated in a cyclotron device at an outside nuclear medicine facility. Thereafter, the FDG is processed to be in a radiopharmaceutical form and is transferred in an individual dose container (i.e., vial, bottle, syringe, etc.) and the container is loaded into a transport pig to prevent unnecessary radiation exposure to personnel, such as the radio-pharmacist, technician, and driver responsible for creation, handling, and transport of the FDG from the cyclotron site to the PET imaging site. Since the half-life of FDG is short, approximately 110 minutes, it is necessary to quickly transport the FDG to the PET imaging site. Depending upon the elapsed transport time and the initial radioactivity level of the FDG at the time of fabrication, the radioactivity level of the FDG may need to be re-measured at the PET imaging site. As an example, if the radioactivity level is too high, the transport radio-pharmacist or a radio-pharmacist at the PET imaging site may be required to dilute the FDG with a diluent dilutent such as, for instance, saline solution, and remove part of the volume or extract fluid to reduce radioactivity prior to patient injection. During this entire process, the handling of FDG from creation to patient injection may be entirely manual. Within this process, shielding products, as described previously (i.e., transport pigs, syringe shields, L-blocks, etc.) are used to shield individuals from FDG. While shielding may reduce the radiation exposure of the radio-pharmacist, the radio-pharmacist may still be exposed to emissions from the radiopharmaceutical agent during the manual mixing, volume reduction, and/or dilution process needed to obtain the required dose. After injection and often after an additional delay to allow the radiopharmaceutical to reach and be absorbed by the desired regions of interest in the body, the patient is typically placed on a moveable bed that slides by remote control into a circular opening of an imaging scanner referred to as the gantry. Positioned around the circular opening and inside the gantry are several rings of radiation detectors. In one type of radiation detector, each detector emits a brief pulse of light every time it is struck with a gamma ray coming from the radionuclide within the patient's body. The pulse of light is amplified by a photomultiplier converted to an electronic signal and the information is sent to the computer that controls the apparatus and records imaging data.
For the sake of completeness, it should be noted that in the United States it also known to have radiopharmaceutical agents delivered in a multi-dose format to the treatment site. As a result, this multi-dose format must be divided into singular doses for individual patients at the treatment site.
The current systems described hereinabove, however, do not provide a system for automatically and continuously monitoring the radioactivity of a radiopharmaceutical within a disposable administration set of a radiopharmaceutical, detect a delivery issue based on the monitored radioactivity of a radiopharmaceutical, and adjust the fluid delivery of the system to cure the delivery issue.